This invention relates to a paint spray gun producing less overspray and therefore providing a cleaner environment.
Every conventional paint spray gun working with compressed air atomizes the paint by the velocity difference of the air leaving the air nozzle and the paint leaving the paint nozzle. Depending upon the air volume, air velocity, expansion, and flow conditions, small, medium and large droplets of paint develop.
Due to the high expansion ratio of the air changing the atmospheric pressure from 15 psi to 100 psi outside of the air nozzle the paint droplets will be atomized. This also results in a fog of paint that will not reach the object to be painted. This overspray contaminates the environment.
It is desirable to form the smallest paint droplets in order to obtain the best finish of the painted surface. The conventional guns working with pressures from 15 psi to 100 psi generally show good atomization, resulting in high overspray since the air is entering the air nozzle at high pressure and expands outside of the air cap.
The low pressure guns already in use work with much lower pressures and corresponding large volume of air. Since the large air volume is flowing through the gun, large air passages are necessary. Due to the low air velocity at the nozzle, resulting from low air pressures, atomization of the paint, in many cases, is not fine enough. This happens particularly with materials of high viscosity or low thinner content.
An object of the present invention is to provide a new paint spray gun to disperse the paint into sufficiently small droplets without forming overspray. As a result, both paint consumption and environmental contamination will be reduced.
A more specific object of the present invention is to provide a new paint spray gun which has a mass flow rate equal to conventional guns but with a larger volume flow.